The present invention generally relates to an electronic control circuit and more particularly relates to an integrated circuit having digital and analog circuitry integrated thereon which are electrically isolated by a voltage regulator.
Conventionally, in an electronic circuit for controlling the operation of a device such as a camera, digital integrated circuitry such as a calculating circuit, and analog integrated circuitry for performing light metering and distance measuring functions, for example, have not been combined in a single integrated circuit, but have instead been formed in different integrated circuits. This is due to the fact that digital and analog circuitry, although capable of being integrated, are fundamentally incompatible in terms of their operating characteristics, power requirements and noise tolerance. Because of this incompatibility, interface circuitry permitting communication between digital circuitry and analog circuitry is usually repaired. Consequently, a large space is needed to accommodate the circuitry, which is extremely disadvantageous in a camera, for example, wherein compactness is of primary importance.
In this connection, it has been proposed in Laid-Open Patent Application No. Hei 1-258459 that digital circuitry, such as a microcomputer for processing digital signals, and analog circuitry, such as a photometer circuit, for processing analog signals, can be constructed within a single chip using CMOS integrated circuit technology and that a power supply for the respective digital and analog circuitry can be commonly shared along with the same power supply for powering the peripheral circuitry, such as a light source, a shutter, a motor, and the like.
In this proposed integrated circuit, in order to shield the analog circuitry from electromagnetic noise produced by the digital circuitry and peripheral circuitry, the digital circuitry and control lines therefor are physically located away from the analog circuitry. In this manner, the performance of the analog circuitry is not deteriorated due to noise caused by the digital circuitry. An electrolytic capacitor is connected outside the integrated circuitry to suppress spurious variation in the power supply voltage supplied to the analog circuitry.
Even when such countermeasures have been taken to eliminate noise as described above, they have not been completely successful. For instance, in cases where the analog circuitry must process signals having a very small amplitude or when the power supply fluctuates due to the operation of the digital circuitry, the performance of the analog circuitry nevertheless deteriorates. Furthermore, when an electrolytic capacitor and a regulator are externally connected, additional mounting space is required and this is also disadvantageous in terms of space.